Purpose This report examines the incidence of and risk factors for strokes that occur in ≥ 5-year survivors of childhood leukemia and brain tumors. Patients and Methods The rate of first occurrence of self-reported late-occurring strokes was determined for leukemia survivors (n = 4,828), brain tumor survivors (n = 1,871), and a comparison group of a random sample of cancer survivor siblings (n = 3,846). Relative risks (RRs) and 95% confidence intervals (CIs) of stroke by treatment exposures were examined by multivariate analyses. Results Thirty-seven leukemia survivors and 63 brain tumor survivors reported a late-occurring stroke. The rate of late-occurring stroke for leukemia survivors was 57.9 per 100,000 person-years (95% CI, 41.2 to 78.7). The RR of stroke for leukemia survivors compared with the sibling comparison group was 6.4 (95% CI, 3.0 to 13.8; P < .0001). The rate of late-occurring stroke for brain tumor survivors was 267.6 per 100,000 person-years (95% CI, 206.8 to 339.2). The RR of stroke for brain tumor survivors compared with the sibling comparison group was 29.0 (95% CI, 13.8 to 60.6; P < .0001). Mean cranial radiation therapy (CRT) dose of ≥ 30 Gy was associated with an increased risk in both leukemia and brain tumor survivors in a dose-dependent fashion, with the highest risk after doses of ≥ 50 Gy CRT. Conclusion Survivors of childhood leukemia and brain tumors, particularly those with brain tumors treated with CRT at doses of greater than 30 Gy, are at an increased risk of stroke.